The present invention relates to an image reading apparatus capable of detecting the distance between a subject and the center of an image reading frame.
In the past, the following two methods have been known for photographing a subject by the use of a video camera and for panning the video camera for the purpose of bringing the subject to the center of an image field or for detecting the distance between the subject and the center of the image field.
(1) A method to detect a position of a subject by using a photocoupler composed of a photoreceptor and a light-emitter and to pan a video camera based upon said position.
(2) A method wherein a reference position (e.g. a matrix in a monitor screen or the like) within an image reading range of a video camera is inputted in advance and a position of a subject contained in image signals is detected electrically and the video camera is panned based on the detected position.
In the aforesaid method (1), an apparatus tends to be large in size because a special sensor for detecting a position is needed in addition to a video camera. Further, the method has its disadvantage that a parallax is caused between the video camera and the position detection sensor.
In the aforesaid method (2), it is impossible to detect position without an absolute reference position, and hereby impossible to calculate an amount of panning. Further, the method has its disadvantage that accuracy of detecting a position is dependent on accuracy of memory to be stored.
The invention has been devised for solving the aforesaid problems and its object is to provide an image reading apparatus wherein it is possible, without requiring any special sensor for detecting a position, to detect a position by utilizing image signals and to control an image reading range.